Can definitions in a dictionary be copyrighted?

Question

Most opening pages in a dictionary say that "copyrighted portions" can not be reproduced, transmitted, etc. Do definitions fall under the "copyrighted portions" of a dictionary?

Best answer will be given among those with citations/sources.

More specifically, Merriam-Webster's Vocabulary Builder. It reads along the lines of "Any of the sections in this book covered by copyright may not be reproduced..."
*Automatic 10 point best answer for listing all:
1. What material within that book is protected by copyright
2. In general, can/are a dictionary's definitions be protected by copyright?
3. Citations/sources for your answers for both of the above

Answer 1

Yes & copied with permission. (But who goes to that extreme?)

Answer 2

unless they go to the effort to cite the creator of each definition, then it can be assumed that the pithy definitions fall short of the definition of "authored work". One or two sentences is not what was intended by the copyright code as a body of work. Now an encyclopedic entry that entails significant depth of original thought and is credited to specific authors would be protected. The copyrighted portions generally refers to the illustrations and art work. Also publications that contain PD material may yet be protected from wholesale replication of the entirety or significant portions by mechanical reproduction.